Cambodian cuisine is an umbrella term for the cuisines of all ethnic groups in Cambodia, whereas Khmer cuisine (សិល្បៈធ្វើម្ហូបខ្មែរ; Khmer culinary art) refers specifically to the more than thousand years old culinary tradition of the Khmer people. Over centuries, Cambodian cuisine has incorporated elements of Indian, Chinese and more recently French cuisine, and due to some of these shared influences and mutual interaction, it has many similarities with the neighbouring Thai, Vietnamese and Lao cuisines. Khmer cuisine can be classified into provincial, elite and royal cuisine, although the difference between the royal and popular cuisine is not as pronounced as in the case of Thailand and Laos. In comparison to the Khmer royal dishes, the elites used less varied and lower quality ingredients. Because of Cambodia's geographic location, rice and fish, especially freshwater fish, are the two most important sources of nutrients in the Cambodian diet. Rice is a staple food generally eaten at every meal. It is believed to have been cultivated by the ancestors of the Khmers in the territory of Cambodia since 5,000 to 2,000 B.C. The advanced hydraulic engineering developed during the Khmer Empire allowed the Khmer to harvest rice and other crops three to four times a year. According to the International Rice Research Institute, there are approximately 2,000 rice varieties indigenous to Cambodia bred over the centuries by the Cambodian rice farmers. One of them – "Malys Angkor" (ម្លិះអង្គរ, Mlih Ángkô) – has been regarded the world's best rice. Khmer cuisine shares some similarities with Indian cuisine as they are both part of the Austroasiatic-speaking group. However, the Mon-Khmer subgroup continued to migrate eastward into Southeast Asia thousands of years ago making them indigenous to the region. Many spices in Khmer cuisine were introduced by the Indian merchants around the 2nd century. The Indian influence on cuisine among other aspects of Khmer culture was already noted by a Chinese visitor around 400 AD.